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<div class="refentry">
<a name="glib-running"></a><div class="titlepage"></div>
<div class="refnamediv"><table width="100%"><tr>
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<h2><span class="refentrytitle">Running GLib Applications</span></h2>
<p>Running GLib Applications — 
How to run and debug your GLib application
</p>
</td>
<td class="gallery_image" valign="top" align="right"></td>
</tr></table></div>
<div class="refsect1">
<a name="id-1.2.7.3"></a><h2>Running and debugging GLib Applications</h2>
<div class="refsect2">
<a name="id-1.2.7.3.2"></a><h3>Environment variables</h3>
<p>
  The runtime behaviour of GLib applications can be influenced by a
  number of environment variables.
</p>
<p><b>Standard variables. </b>
    GLib reads standard environment variables like <code class="envar">LANG</code>,
    <code class="envar">PATH</code>, <code class="envar">HOME</code>, <code class="envar">TMPDIR</code>,
    <code class="envar">TZ</code> and <code class="envar">LOGNAME</code>.
  </p>
<p><b>XDG directories. </b>
    GLib consults the environment variables <code class="envar">XDG_DATA_HOME</code>,
    <code class="envar">XDG_DATA_DIRS</code>, <code class="envar">XDG_CONFIG_HOME</code>,
    <code class="envar">XDG_CONFIG_DIRS</code>, <code class="envar">XDG_CACHE_HOME</code> and
    <code class="envar">XDG_RUNTIME_DIR</code> for the various XDG directories.
    For more information, see the <a class="ulink" href="http://standards.freedesktop.org/basedir-spec/basedir-spec-latest.html" target="_top">XDG basedir spec</a>.
  </p>
<p><a name="G_FILENAME_ENCODING"></a><b><code class="envar">G_FILENAME_ENCODING</code>. </b>
    This environment variable can be set to a comma-separated list of character
    set names. GLib assumes that filenames are encoded in the first character
    set from that list rather than in UTF-8. The special token "@locale" can be
    used to specify the character set for the current locale.
  </p>
<p><a name="G_BROKEN_FILENAMES"></a><b><code class="envar">G_BROKEN_FILENAMES</code>. </b>
    If this environment variable is set, GLib assumes that filenames are in
    the locale encoding rather than in UTF-8. G_FILENAME_ENCODING takes
    priority over G_BROKEN_FILENAMES.
  </p>
<p><a name="G_MESSAGES_PREFIXED"></a><b><code class="envar">G_MESSAGES_PREFIXED</code>. </b>
    A list of log levels for which messages should be prefixed by the
    program name and PID of the application. The default is to prefix
    everything except <code class="literal">G_LOG_LEVEL_MESSAGE</code> and
    <code class="literal">G_LOG_LEVEL_INFO</code>.
    The possible values are
    <code class="literal">error</code>,
    <code class="literal">warning</code>,
    <code class="literal">critical</code>,
    <code class="literal">message</code>,
    <code class="literal">info</code> and
    <code class="literal">debug</code>.
    You can also use the special values
    <code class="literal">all</code> and
    <code class="literal">help</code>.
  
    This environment variable only affects the default log handler,
    g_log_default_handler().
  </p>
<p><a name="G_MESSAGES_DEBUG"></a><b><code class="envar">G_MESSAGES_DEBUG</code>. </b>
    A space-separated list of log domains for which informational
    and debug messages should be printed. By default, these
    messages are not printed.
  
    You can also use the special value <code class="literal">all</code>.
  
    This environment variable only affects the default log handler,
    g_log_default_handler().
  </p>
<p><a name="G-DEBUG:CAPS"></a><b><code class="envar">G_DEBUG</code>. </b>
    This environment variable can be set to a list of debug options,
    which cause GLib to print out different types of debugging information.
    </p>
<div class="variablelist"><table border="0" class="variablelist">
<colgroup>
<col align="left" valign="top">
<col>
</colgroup>
<tbody>
<tr>
<td><p><span class="term">fatal-warnings</span></p></td>
<td><p>Causes GLib to abort the program at the first call
           to g_warning() or g_critical().</p></td>
</tr>
<tr>
<td><p><span class="term">fatal-criticals</span></p></td>
<td><p>Causes GLib to abort the program at the first call
           to g_critical().</p></td>
</tr>
<tr>
<td><p><span class="term">gc-friendly</span></p></td>
<td><p>Newly allocated memory that isn't directly initialized,
          as well as memory being freed will be reset to 0. The point here is
          to allow memory checkers and similar programs that use Boehm GC alike
          algorithms to produce more accurate results.</p></td>
</tr>
<tr>
<td><p><span class="term">resident-modules</span></p></td>
<td><p>All modules loaded by GModule will be made resident.
          This can be useful for tracking memory leaks in modules which are
          later unloaded; but it can also hide bugs where code is accessed
          after the module would have normally been unloaded.</p></td>
</tr>
<tr>
<td><p><span class="term">bind-now-modules</span></p></td>
<td><p>All modules loaded by GModule will bind their symbols
          at load time, even when the code uses %G_MODULE_BIND_LAZY.</p></td>
</tr>
</tbody>
</table></div>
<p>
    The special value all can be used to turn on all debug options.
    The special value help can be used to print all available options.
  </p>
<p><a name="G_SLICE"></a><b><code class="envar">G_SLICE</code>. </b>
    This environment variable allows reconfiguration of the GSlice
    memory allocator.
    </p>
<div class="variablelist"><table border="0" class="variablelist">
<colgroup>
<col align="left" valign="top">
<col>
</colgroup>
<tbody>
<tr>
<td><p><span class="term">always-malloc</span></p></td>
<td><p>This will cause all slices allocated through
          g_slice_alloc() and released by g_slice_free1() to be actually
          allocated via direct calls to g_malloc() and g_free().
          This is most useful for memory checkers and similar programs that
          use Boehm GC alike algorithms to produce more accurate results.
          It can also be in conjunction with debugging features of the system's
          malloc() implementation such as glibc's MALLOC_CHECK_=2 to debug
          erroneous slice allocation code, although
          <code class="literal">debug-blocks</code> is usually a better suited debugging
          tool.</p></td>
</tr>
<tr>
<td><p><span class="term">debug-blocks</span></p></td>
<td>
<p>Using this option (present since GLib 2.13) engages
          extra code which performs sanity checks on the released memory
          slices. Invalid slice addresses or slice sizes will be reported and
          lead to a program halt. This option is for debugging scenarios.
          In particular, client packages sporting their own test suite should
          <span class="emphasis"><em>always enable this option when running tests</em></span>.
          Global slice validation is ensured by storing size and address
          information for each allocated chunk, and maintaining a global
          hash table of that data. That way, multi-thread scalability is
          given up, and memory consumption is increased. However, the
          resulting code usually performs acceptably well, possibly better
          than with comparable memory checking carried out using external
          tools.</p>
<p>An example of a memory corruption scenario that cannot be
          reproduced with <code class="literal">G_SLICE=always-malloc</code>, but will
          be caught by <code class="literal">G_SLICE=debug-blocks</code> is as follows:
          </p>
<pre class="programlisting">
            void *slist = g_slist_alloc (); /* void* gives up type-safety */
            g_list_free (slist);            /* corruption: sizeof (GSList) != sizeof (GList) */
          </pre>
</td>
</tr>
</tbody>
</table></div>
<p>
    The special value all can be used to turn on all options.
    The special value help can be used to print all available options.
  </p>
<p><a name="G_RANDOM_VERSION"></a><b><code class="envar">G_RANDOM_VERSION</code>. </b>
    If this environment variable is set to '2.0', the outdated
    pseudo-random number seeding and generation algorithms from
    GLib 2.0 are used instead of the newer, better ones. You should
    only set this variable if you have sequences of numbers that were
    generated with Glib 2.0 that you need to reproduce exactly.
  </p>
<p><a name="LIBCHARSET_ALIAS_DIR"></a><b><code class="envar">LIBCHARSET_ALIAS_DIR</code>. </b>
    Allows to specify a nonstandard location for the
    <code class="filename">charset.aliases</code> file that is used by the
    character set conversion routines. The default location is the
    <em class="replaceable"><code>libdir</code></em> specified at compilation time.
  </p>
<p><a name="TZDIR"></a><b><code class="envar">TZDIR</code>. </b>
    Allows to specify a nonstandard location for the timezone data files
    that are used by the #GDateTime API. The default location is under
    <code class="filename">/usr/share/zoneinfo</code>. For more information,
    also look at the <span class="command"><strong>tzset</strong></span> manual page.
  </p>
</div>
<hr>
<div class="refsect2">
<a name="setlocale"></a><h3>Locale</h3>
<p>
A number of interfaces in GLib depend on the current locale in which
an application is running. Therefore, most GLib-using applications should
call <code class="function">setlocale (LC_ALL, "")</code> to set up the current
locale.
</p>
<p>
On Windows, in a C program there are several locale concepts
that not necessarily are synchronized. On one hand, there is the
system default ANSI code-page, which determines what encoding is used
for file names handled by the C library's functions and the Win32
API. (We are talking about the "narrow" functions here that take
character pointers, not the "wide" ones.)
</p>
<p>
On the other hand, there is the C library's current locale. The
character set (code-page) used by that is not necessarily the same as
the system default ANSI code-page. Strings in this character set are
returned by functions like <code class="function">strftime()</code>.
</p>
</div>
<p>
glib ships with a set of python macros for the gdb debugger. These includes pretty
printers for lists, hashtables and gobject types. It also has a backtrace filter
that makes backtraces with signal emissions easier to read.
</p>
<p>
To use this you need a recent enough gdb that supports python scripting. Gdb 7.0
should be recent enough, but branches of the "archer" gdb tree as used in Fedora 11
and Fedora 12 should work too. You then need to install glib in the same prefix as
gdb so that the python gdb autoloaded files get installed in the right place for
gdb to pick up.
</p>
<p>
General pretty printing should just happen without having to do anything special.
To get the signal emission filtered backtrace you must use the "new-backtrace" command
instead of the standard one.
</p>
<p>
There is also a new command called gforeach that can be used to apply a command
on each item in a list. E.g. you can do
</p>
<pre class="programlisting">
gforeach i in some_list_variable: print *(GtkWidget *)l
</pre>
<p>
Which would print the contents of each widget in a list of widgets.
</p>
<hr>
<div class="refsect2">
<a name="id-1.2.7.3.8"></a><h3>SystemTap</h3>
<p>
<a class="ulink" href="http://sourceware.org/systemtap/" target="_top">SystemTap</a> is a dynamic whole-system
analysis toolkit.  GLib ships with a file <code class="filename">glib.stp</code> which defines a
set of probe points, which you can hook into with custom SystemTap scripts.
See the files <code class="filename">glib.stp</code> and <code class="filename">gobject.stp</code> which
are in your shared SystemTap scripts directory.
</p>
</div>
<hr>
<div class="refsect2">
<a name="id-1.2.7.3.9"></a><h3>Memory statistics</h3>
<p>
g_mem_profile() will output a summary g_malloc() memory usage, if memory
profiling has been enabled by calling
<code class="literal">g_mem_set_vtable (glib_mem_profiler_table)</code> upon startup.
</p>
<p>
If GLib has been configured with <code class="option">--enable-debug=yes</code>,
then g_slice_debug_tree_statistics() can be called in a debugger to
output details about the memory usage of the slice allocator.
</p>
</div>
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